This invention relates to an air/fuel ratio correcting device for an internal combustion engine, which is adapted to correct the air/fuel ratio of an air/fuel mixture being supplied to the engine, depending upon the intake air temperature, so as to maintain the air/fuel ratio to a desired value.
A fuel supply control system adapted for use with an internal combustion engine, particularly a gasoline engine has been proposed e.g. by U.S. Ser. No. 348,648 now U.S. Pat. No. 4,445,483 assigned to the assignee of the present application, which is adapted to determine the valve opening period of a fuel injection device for control of the fuel injection quantity, i.e. the air/fuel ratio of an air/fuel mixture being supplied to the engine, by first determining a basic value of the above valve opening period as a function of engine rpm and intake pipe absolute pressure and then adding to and/or multiplying same by constants and/or coefficients being functions of engine rpm, intake pipe absolute pressure, engine temperature, throttle valve opening, exhaust gas ingredient concentration (oxygen concentration), etc., by electronic computing means.
In internal combustion engines, the density of the intake air varies with a change in the intake air temperature. This causes a change in the mass flow rate of the intake air even when there is no change in the volumetric flow rate of the intake air or in the absolute pressure in the intake pipe, leading to a change in the air/fuel ratio of the mixture being supplied to the engine. Further, the evaporation rate of fuel decreases with a decrease in the intake air temperature. Therefore, when the intake air temperature is low, the air/fuel ratio can be leaner than a desired value. In order to maintain the air/fuel ratio at values appropriate for operating conditions of the engine by means of the aforementioned fuel supply control system, it is necessary to correct the quantity of fuel being supplied to the engine in response to changes in the intake air temperature.